Hot Oxygen Atoms Research Articles

Mars Hot Oxygen Density and Effective Temperature Derived From the MAVEN IUVS Observations

AbstractThe escape of hot oxygen atoms from Mars is important for the evolution of the planet's H2O and CO2 inventories. Owing to the lack of data constraints prior to the Mars Atmosphere and Volatile Evolution (MAVEN) mission, previous understanding of this key loss channel of the Mars atmosphere relied mostly on physics‐based models. Using the optical observations from the MAVEN Imaging Ultraviolet Spectrograph (IUVS) during 2014–2018, we perform the first inversion analysis of the coronal scans at 130.4 nm to quantify the density and effective temperature of the Mars hot oxygen corona. Our results indicate that the exobase densities of the hot oxygen atoms are ∼6.3–8.0 × 103 and ∼1.2 × 104 cm−3 during low and moderate solar activities, respectively, which agree well with recent empirical estimates using MAVEN's in situ measurements and, however, are about a factor of two higher than previous model predictions. The effective temperature varies only slightly between ∼4100–4500 K. The temperature and density variations with solar, seasonal, and dust conditions are consistent with previous models. Comparison with inversion results from IUVS limb scans indicates that the cold and the hot oxygen populations dominate below ∼200 and above ∼600 km, respectively, between which the kinetic distribution depends on both populations. Our results demonstrate for the first time the feasibility of extracting information about the Mars hot oxygen corona directly from optical observations, opening up a powerful means for monitoring the Mars oxygen escape on a global scale in future missions.

Quantum scattering cross-sections for O(3P) + N2 collisions for planetary aeronomy

ABSTRACT ‘Hot atoms’, atoms in their excited states, transfer their energy to the surrounding atmosphere through collisions. This process (known as thermalization) plays a crucial role in various astrophysical and atmospheric processes. Thermalization of hot atoms is mainly governed by the amount of species present in the surrounding atmosphere and the collision cross-sections between the hot atoms and surrounding species. In this work, we investigated the elastic and inelastic collisions between hot oxygen atoms and neutral N2 molecules, relevant to oxygen gas escape from the Martian atmosphere and for characterizing the chemical reactions in hypersonic flows. We conducted a series of quantum scattering calculations between various isotopes of O(3P) atoms and N2 molecules across a range of collision energies (0.3–4 eV), and computed both their differential and collision cross-sections using quantum time-independent coupled-channel approach. Our differential cross-section results indicate a strong preference for forward scattering over sideways or backward scattering, and this anisotropy in scattering is further pronounced at higher collision energies. By comparing the cross-sections of three oxygen isotopes, we find that the heavier isotopes consistently have larger collision cross-sections than the lighter isotopes. As a whole, this study contributes to a better understanding of the energy distribution and thermalization processes of hot atoms within atmospheric environments. Specifically, the cross-sectional data presented in this work is directly useful in improving the accuracy of energy relaxation modelling of O and N2 collisions over the Mars and Venus atmospheres.

Modeling Equilibration Dynamics of Hyperthermal Products of Surface Reactions Using Scalable Neural Network Potential with First-Principles Accuracy.

Equilibration dynamics of hot oxygen atoms following the dissociation of O2 on Pd(100) and Pd(111) surfaces are investigated by molecular dynamics simulations based on a scalable neural network potential enabling first-principles description of the interaction of O2 and O interacting with variable Pd supercells. By analyzing hundreds of trajectories with appropriate initial sampling, the measured distance distribution of equilibrated atom pairs on Pd(111) is well reproduced. However, our results on Pd(100) suggest that the ballistic motion of hot atoms predicted previously is a rare event under ideal conditions, while initial molecular orientation and surface thermal fluctuation could significantly affect the overall postdissociation dynamics. On both surfaces, dissociated hyperthermal oxygen atoms primarily locate their nascent positions and experience a similar random walk motion nearby.

Atmospheric Loss of Atomic Oxygen during Proton Aurorae on Mars

—For the first time, the calculations of the penetration of protons of the undisturbed solar wind into the daytime atmosphere of Mars due to charge exchange in the extended hydrogen corona (Shematovich et al., 2021) are used allowing us to determine self-consistently the sources of suprathermal oxygen atoms, as well as their kinetics and transport. An additional source of hot oxygen atoms—collisions accompanied by the momentum and energy transfer from the flux of precipitating high-energy hydrogen atoms to atomic oxygen in the upper atmosphere of Mars—was included in the Boltzmann kinetic equation, which was solved with the Monte-Carlo kinetic model. As a result, the population of the hot oxygen corona of Mars has been estimated; and it has been shown that the proton aurorae are accompanied by the atmospheric loss of atomic oxygen, which is evaluated within a range of (3.5–5.8) × 107 cm–2 s–1. It has been shown that the exosphere becomes populated with a substantial amount of suprathermal oxygen atoms with kinetic energies up to the escape energy, 2 eV. The atomic oxygen loss rate caused by a sporadic source in the Martian atmosphere—the precipitation of energetic neutral atoms of hydrogen (H‑ENAs) during proton aurorae at Mars—was estimated by the self-consistent calculations according to a set of the Monte-Carlo kinetic models. These values turned out be comparable to the atomic oxygen loss supported by a regular source—the exothermic photochemical reactions (Groeller et al., 2014; Jakosky et al., 2018). It is currently supposed that the atmospheric loss of Mars due to the impact of the solar wind plasma and, in particular, the fluxes of precipitating high-energy protons and hydrogen atoms during solar flares and coronal mass ejections may play an important role in the loss of the neutral atmosphere on astronomic time scales (Jakosky et al., 2018).

Hydrogen and helium escape on Venus via energy transfer from hot oxygen atoms

ABSTRACT Due to the relatively strong gravity on Venus, heavy atmospheric neutrals are difficult to accelerate to the escape velocity. However, a variety of processes, such as the dissociative recombination of ionospheric O$_2^+$, are able to produce hot atoms which could deliver a significant amount of energy to light neutrals and drive their escape. In this study, we construct a Monte Carlo model to simulate atmospheric escape of three light species, H, H2, and He, on Venus via such a knock-on process. Two Venusian background atmosphere models are adopted, appropriate for solar minimum and maximum conditions. Various energy-dependent and species-dependent cross-sections, along with a common strongly forward scattering angle distribution, are used in our calculations. Our model results suggest that knock-on by hot O likely plays the dominant role in driving total atmospheric hydrogen and helium escape on Venus at the present epoch, with a significant portion contributed from regions below the exobase. Substantial variations are also revealed by our calculations. Of special interest is the modelled reduction in escape flux at high solar activities for all species, mainly associated with the enhancement in thermal O concentration near the exobase at high solar activities which hinders escape. Finally, model uncertainties due to several controlling factors, including the distribution of relevant light species in the background atmosphere, the plane-parallel approximation, and the finite O energy distribution, are evaluated.

Monte Carlo Calculations of Helium Escape on Mars via Energy Transfer from Hot Oxygen Atoms

Abstract Understanding He escape is crucial for deciphering the evolution of the He budget on Mars. A number of viable mechanisms have been proposed to drive He escape, with energy transfer from hot O generally thought to be the dominant one. This study is devoted to a state-of-the-art evaluation of the above process assuming hot O is exclusively produced from the dissociative recombination of O2 + in the Martian ionosphere. A Monte Carlo model is constructed, with model inputs optimized by the recent Mars Atmosphere and Volatile Evolution measurements. The model calculations reveal a dayside He escape flux of (1–2) × 106 cm−2 s−1 referred to the surface, for a possible range of H2 mixing ratio at an altitude of 80 km from 0 to 40 ppm. The computed He escape flux increases with increasing nascent O energy and decreasing atmospheric H2 and H abundances. The portion of the atmosphere below the exobase is found to make an exceptionally large contribution of 95% to He escape.

Oxygen Atom Escape from the Martian Atmosphere during Proton Auroral Events

We present the model calculation results of the atomic oxygen loss rate from the Martian atmosphere induced by precipitation of high-energy protons and hydrogen atoms (H/H+) from the solar wind plasma. Penetration of energetic protons and hydrogen atoms from the solar wind plasma to the upper atmosphere of Mars at altitudes of 100−250 km is accompanied by the momentum and energy transfer in collisions with the main component, atomic oxygen. This process is considered as atmospheric gas sputtering during proton auroral events, which is accompanied by formation of the suprathermal hydrogen and oxygen atom fluxes escaping from the atmosphere. When calculating the formation rate of suprathermal atoms, the modified Monto Carlo kinetic model was used. This model was earlier developed to analyze the data of the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) and the Solar Wind Ion Analyzer (SWIA) onboard the Mars Express (MEX) and the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, respectively. We study the processes of kinetics and transport of hot oxygen atoms in the transition zone (from the thermosphere to the exosphere) of Mars’ upper atmosphere. The kinetic energy distribution functions for suprathermal oxygen atoms were calculated. It has been shown that, during proton auroral events on Mars, the exosphere is populated with a significant number of suprathermal oxygen atoms, the kinetic energy of which reaches the escape energy, 2 eV. In addition to photochemical sources, a hot fraction is formed in the oxygen corona; and a nonthermal flux of atomic oxygen escaping from the Martian atmosphere is produced during proton aurora events. Proton aurorae are sporadic auroral events. Consequently, according to the estimates obtained from the recent MAVEN observations the magnitude of the precipitation-induced escaping flux of hot oxygen atoms may become prevailing over the photochemical sources under conditions of the extreme solar events such as solar flares and coronal mass ejections.

Suprathermal oxygen atoms in the Martian upper atmosphere: Contribution of the proton and hydrogen atom precipitation

This is a study of the kinetics and transport of hot oxygen atoms in the transition region (from the thermosphere to the exosphere) of the Martian upper atmosphere. It is assumed that the source of the hot oxygen atoms is the transfer of momentum and energy in elastic collisions between thermal atmospheric oxygen atoms and the high-energy protons and hydrogen atoms precipitating onto the Martian upper atmosphere from the solar-wind plasma. The distribution functions of suprathermal oxygen atoms by the kinetic energy are calculated. It is shown that the exosphere is populated by a large number of suprathermal oxygen atoms with kinetic energies up to the escape energy 2 eV; i.e., a hot oxygen corona is formed around Mars. The transfer of energy from the precipitating solar-wind plasma protons and hydrogen atoms to the thermal oxygen atoms leads to the formation of an additional nonthermal escape flux of atomic oxygen from the Martian atmosphere. The precipitation-induced escape flux of hot oxygen atoms may become dominant under the conditions of extreme solar events, such as solar flares and coronal mass ejections, as shown by recent observations onboard NASA’s MAVEN spacecraft (Jakosky et al., 2015).

Escape and evolution of Mars's CO2 atmosphere: Influence of suprathermal atoms

AbstractWith a Monte Carlo model we investigate the escape of hot oxygen and carbon from the Martian atmosphere for four points in time in its history corresponding to 1, 3, 10, and 20 times the present solar EUV flux. We study and discuss different sources of hot oxygen and carbon atoms in the thermosphere and their changing importance with the EUV flux. The increase of the production rates due to higher densities resulting from the higher EUV flux competes against the expansion of the thermosphere and corresponding increase in collisions. We find that the escape due to photodissociation increases with increasing EUV level. However, for the escape via some other reactions, e.g., dissociative recombination of , this is only true until the EUV level reaches 10 times the present EUV flux and then the rates start to decrease. Furthermore, our results show that Mars could not have had a dense atmosphere at the end of the Noachian epoch, since such an atmosphere would not have been able to escape until today. In the pre‐Noachian era, most of the magma ocean and volcanic activity‐related outgassed CO2 atmosphere could have been lost thermally until the Noachian epoch, when nonthermal loss processes such as suprathermal atom escape became dominant. Thus, early Mars could have been hot and wet during the pre‐Noachian era with surface CO2 pressures larger than 1 bar during the first 300 Myr after the planet's origin.

Photochemical escape of oxygen from Mars: First results from MAVEN in situ data

AbstractPhotochemical escape of atomic oxygen is thought to be one of the dominant channels for Martian atmospheric loss today and played a potentially major role in climate evolution. Mars Atmosphere and Volatile Evolution Mission (MAVEN) is the first mission capable of measuring, in situ, the relevant quantities necessary to calculate photochemical escape fluxes. We utilize 18 months of data from three MAVEN instruments: Langmuir Probe and Waves, Neutral Gas and Ion Mass Spectrometer, and SupraThermal And Thermal Ion Composition. From these data, we calculate altitude profiles of the production rate of hot oxygen atoms from the dissociative recombination of O2+ and the probability that such atoms will escape the Mars atmosphere. From this, we determine escape fluxes for 815 periapsis passes. Derived average dayside hot O escape rates range from 1.2 to 5.5 × 1025 s−1, depending on season and EUV flux, consistent with several pre‐MAVEN predictions and in broad agreement with estimates made with other MAVEN measurements. Hot O escape fluxes do not vary significantly with dayside solar zenith angle or crustal magnetic field strength but depend on CO2 photoionization frequency with a power law whose exponent is 2.6 ± 0.6, an unexpectedly high value which may be partially due to seasonal and geographic sampling. From this dependence and historical EUV measurements over 70 years, we estimate a modern‐era average escape rate of 4.3 × 1025 s−1. Extrapolating this dependence to early solar system, EUV conditions gives total losses of 13, 49, 189, and 483 mbar of oxygen over 1–3 and 3.5 Gyr, respectively, with uncertainties significantly increasing with time in the past.

MAVEN insights into oxygen pickup ions at Mars

AbstractSince Mars Atmosphere and Volatile EvolutioN (MAVEN)'s arrival at Mars on 21 September 2014, the SEP (Solar Energetic Particle) instrument on board the MAVEN spacecraft has been detecting oxygen pickup ions with energies of a few tens of keV up to ~200 keV. These ions are created in the distant upstream part of the hot atomic oxygen exosphere of Mars, via photoionization, charge exchange with solar wind protons, and electron impact. Once ionized, atomic oxygen ions are picked up by the solar wind and accelerated downstream, reaching energies high enough for SEP to detect them. We model the flux of oxygen pickup ions observed by MAVEN SEP in the undisturbed upstream solar wind and compare our results with SEP's measurements. Model‐data comparisons of SEP fluxes confirm that pickup oxygen associated with the Martian exospheric hot oxygen is indeed responsible for the MAVEN SEP observations.

Suprathermal oxygen and hydrogen atoms in the upper Martian atmosphere

The processes of kinetics and transport of hot oxygen and hydrogen atoms in the transition (from the thermosphere to the exosphere) region of the upper Martian atmosphere are studied. The reaction of dissociative recombination of the principal ionospheric ion O2+ with thermal electrons in the ionosphere of Mars served as the source of hot oxygen atoms. The process of momentum and energy transfer in elastic collisions between hot oxygen atoms and atmospheric hydrogen atoms with thermal energies was regarded as the source of hot hydrogen atoms. The kinetic energy distribution functions are determined for suprathermal oxygen and hydrogen atoms. It is shown that the exosphere is populated with a significant number of suprathermal oxygen atoms with kinetic energies ranging up to the escape energy of 2 eV (i.e., the hot oxygen Martian corona is formed). The transfer of energy from hot oxygen atoms to thermal hydrogen atoms creates an additional nonthermal flux of atomic hydrogen escaping from the Martian atmosphere.

Non‐thermal escape of molecular hydrogen from Mars

We present a detailed theoretical analysis of non‐thermal escape of molecular hydrogen from Mars induced by collisions with hot atomic oxygen from the Martian corona. To accurately describe the energy transfer in O + H2(v, j) collisions, we performed extensive quantum‐mechanical calculations of state‐to‐state elastic, inelastic, and reactive cross sections. The escape flux of H2molecules was evaluated using a simplified 1D column model of the Martian atmosphere with realistic densities of atmospheric gases and hot oxygen production rates for low solar activity conditions. An average intensity of the non‐thermal escape flux of H2 of 1.9 × 105 cm−2s−1 was obtained considering energetic O atoms produced in dissociative recombinations of O2+ions. Predicted ro‐vibrational distribution of the escaping H2was found to contain a significant fraction of higher rotational states. While the non‐thermal escape rate was found to be lower than Jeans rate for H2molecules, the non‐thermal escape rates of HD and D2 are significantly higher than their respective Jeans rates. The accurate evaluation of the collisional escape flux of H2and its isotopes is important for understanding non‐thermal escape of molecules from Mars, as well as for the formation of hot H2 Martian corona. The described molecular ejection mechanism is general and expected to contribute to atmospheric escape of H2 and other light molecules from planets, satellites, and exoplanetary bodies.

Energy transfer in O collisions with He isotopes and Helium escape from Mars

[1] Accurate data on energy-transfer collisions between hot oxygen atoms and the atmospheric helium gas on Mars, are reported. Anisotropic cross sections for elastic collisions of O(3P) and O(1D) atoms with helium gas have been calculated quantum mechanically and found to be surprisingly similar. Cross sections, computed for collisions with both helium isotopes, 3He and 4He, have been used to construct the kernel of the Boltzmann equation describing the energy relaxation of hot oxygen atoms. Computed rates of energy transfer in O+He collisions have been used to evaluate the flux of He atoms escaping from the Mars atmosphere. Atmospheric layers mostly responsible for production of the He escape flux are identified. Our results demonstrate that strong angular anisotropy of scattering cross sections increases the collisional ejection of light atoms and is critical in the evaluation of He escape from Mars, Venus and Earth.

Venus' atomic hot oxygen environment

We present a Monte Carlo study of the atomic hot oxygen corona of Venus. In this model we consider elastic, inelastic, and quenching collisions between the traced hot particle and the ambient neutral atmosphere as well as differential cross sections to determine the scattering angle in the collisions. We also include rotational and vibrational excitation energies for the calculation of the initial energy of the produced hot oxygen atoms. Our results indicate that the differential cross sections and the fraction between elastic, inelastic, and quenching collisions are the most sensitive parameters which effect the corona density. We found that the hot O densities inferred from PVO observations can only be reproduced during high solar activity based on a forward scattering model but without inelastic and quenching collisions. The corona densities for low solar activity (VEX solar conditions) are about a factor of 2–3 smaller than for high solar activity.

Three‐dimensional study of Mars upper thermosphere/ionosphere and hot oxygen corona: 1. General description and results at equinox for solar low conditions

Unlike Earth and Venus, Mars with a weak gravity allows an extended corona of hot species and the escape of its lighter constituents in its exosphere. Being the most important reaction, the dissociative recombination of O2+ is responsible for most of the production of hot atomic oxygen deep in the dayside thermosphere/ionosphere. The investigation of the Martian upper atmosphere is therefore complicated by the change in the flow regime from a collisional to a collisionless domain. Past studies, which used simple extrapolations of 1‐D thermospheric/ionospheric parameters, could not account for the full effects of realistic conditions, which are shown to be of significant influence on the exosphere both close to and far away from the exobase. In this work, the combination of the new 3‐D Direct Simulation Monte Carlo kinetic model and the modern 3‐D Mars Thermosphere General Circulation Model is employed to describe self‐consistently the Martian upper atmosphere at equinox for solar low conditions. For the first time, a 3‐D analysis and shape of the Martian hot corona is provided, along with density and temperature profiles of cold and hot constituents as functions of position on the planet. Atmospheric loss and ion production (found to be more than an order of magnitude lower than the neutral escape), calculated locally all around the planet, provide valuable information for plasma models, refining the understanding of the ion loss, atmospheric sputtering, and interaction with the solar wind, in general.

On the elusive hot oxygen corona of Venus

After more than two years in orbit still no Venus Express observations were published concerning the hot oxygen corona of Venus which could verify the corresponding controversial observations of Venera 11 and PVO, three decades ago. Based on recent energy and mass dependent collision cross sections, the energy distributions of hot atomic oxygen created via dissociative recombination of O2+ are calculated in the daytime thermosphere by means of a 3D Monte Carlo approach. The exosphere density is obtained from the corresponding energy density and angular distribution at 240 km altitude by using a test particle model which traces the ballistic trajectories of hot O atoms in the exosphere. Our study indicates that upon taking into account proper input parameters, the hot oxygen corona appears to be substantially less dense than suggested by previous simulations.

Solar‐wind control of the hot oxygen corona around Mars

The global behavior and escape rate of hot oxygen atoms around Mars and their response to different solar wind dynamic pressure (PSW) conditions are investigated using a multidimensional time‐dependent magnetosheath‐ionosphere‐exosphere (Msh‐I‐E) coupling model. Recently we reported that an increase in PSW leads to a short‐term increase in the escape rate of nonthermal oxygen using a one‐dimensional (1‐D) Msh‐I‐E model. The model used in the present paper is a multidimensional version of our previous 1‐D model. For the exosphere model, we adopt a three‐dimensional Monte Carlo approach above a 250‐km altitude, while a time‐dependent two‐stream approach is employed below 250 km. The exosphere model is coupled with a two‐dimensional resistive magnetohydrodynamic model of the magnetosheath‐ionosphere interaction, assuming axial symmetry with respect to the Sun‐Mars line. The results of the present model are consistent with the results of the 1‐D model. The escape rate of hot oxygen for PSW = 0.36 nPa is roughly twice that for PSW = 1.43 nPa under steady state conditions. For nonstationary conditions, where PSW is suddenly increased from 0.36 to 1.43 nPa, the escape rate is temporarily enhanced by a factor of 2.3 to 4.5 compared with that of the steady state case. The hot oxygen density is found to be less dependent on PSW than is the escape rate.

A study of suprathermal oxygen atoms in Mars upper thermosphere and exosphere over the range of limiting conditions

As a part of a global effort, the dynamics of energetic particles flowing through the martian upper atmosphere is studied. Most of the production of hot atomic oxygen occurs deep in the day-side thermosphere of Mars, where dissociative recombination (DR) of O 2 + ion is the dominant source. The study of an upper atmosphere is complicated by the change in the flow regime from a thermospheric collisional to an exospheric collisionless domain. To understand the martian exosphere, it is then highly desirable to employ a global kinetic model that includes a self-consistent description of both thermospheric and exospheric regions. In this work, a combination of our Direct Simulation Monte Carlo (DSMC) model [Tenishev, V., Combi, M.R., 2005. Monte-Carlo model for dust/gas interaction in rarefied flows. AIAA, 2005–4832] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S.W., Bell, J.M., Murphy, J.R., Lopez-Valverde, M.A., Withers, P.G., 2006. Geophys. Res. Lett. 32, doi:10.1029/2005GL024059. L02203] is used to describe self-consistently the exosphere and the upper thermosphere. Along with the effect of ionization, the model provides profiles of density and temperature, atmospheric loss rates and return fluxes as functions of the Solar Zenith Angle (SZA) for all cases considered. To present a complete description of the effects of a 3D thermosphere onto the exosphere, several of the most limiting cases spanning spatial and temporal domains are examined. Along with solar activity variability, the influences of position on the planet and of different seasons are investigated and their relative contribution to the atmospheric loss is shown to be of the same order.

Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space

A three‐dimensional (3‐D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O2+between 120 and 300 km and the sputtering of the Martian atmosphere by incident O+pickup ions. The reimpacting and escaping fluxes of pickup ions are derived from a 3‐D hybrid model describing the interaction of the solar wind with our computed Martian oxygen exosphere. In this work it is shown that the role of the sputtering crucially depends on an accurate description of the Martian corona as well as of its interaction with the solar wind. The sputtering contribution to the total oxygen escape is smaller by one order of magnitude than the contribution due to the dissociative recombination. The neutral escape is dominant at both solar activities (1 × 1025s−1for low solar activity and 4 × 1025s−1for high solar activity), and the ion escape flux is estimated to be equal to 2 × 1023s−1at low solar activity and to 3.4 × 1024s−1at high solar activity. This work illustrates one more time the strong dependency of these loss rates on solar conditions. It underlines the difficulty of extrapolating the present measured loss rates to the past solar conditions without a better theoretical and observational knowledge of this dependency.